Open Paleo

Ratchasimasaurus

Shibata et al., 2011 rat-KAS-ee-muh-SOR-us

Named after Nakhon Ratchasima province in Thailand where the fossil was found, combined with Greek sauros (lizard); meaning "Nakhon Ratchasima lizard".

121.4–113.2 million years ago Aptian, Early Cretaceous
Early Cretaceous stages

Ratchasimasaurus is a genus of iguanodontian ornithopod dinosaur from Early Cretaceous (Aptian stage) Khok Kruat Formation of Nakhon Ratchasima province in northeastern Thailand. The type and only species is R. suranareae, named after Thao Suranari, a 19th-century war heroine. It is diagnosed by a uniquely elongated, dorsoventrally compressed dentary ramus, though one study regarded the genus as a nomen dubium on the grounds that its characters are widespread in Styracosterna.

Under dispute

Ratchasimasaurus suranareae is diagnosed by an elongate, dorsoventrally compressed dentary ramus (Shibata and colleagues, 2011), whose describers considered it a basal non-hadrosaurid iguanodontian. The one analysis that resolves it recovers it within Hadrosauroidea, paired with Proa (Madzia and colleagues, 2019).

Diagnosis

  1. Proportionally elongated and flat dentary with length/height ratio > 6 (6.9 in holotype)
  2. Dorsoventrally compressed dentary ramus, unique among Iguanodontia
  3. Caudally inclined coronoid process
  4. Buccal shelf present between coronoid process and caudal tooth row
  5. Alveolar trough molded to tooth crown and root shape
  6. Short diastema between predentary attachment and first alveolus

Species

Ratchasimasaurus suranareae Shibata et al., 2011

Type species

Named for Thao Suranari, a 19th-century Thai war heroine celebrated in Nakhon Ratchasima Province, where the fossil was discovered.

Holotype
NRRU-A2064 , Nakhon Ratchasima Rajabhat University
Material
Complete left dentary 198.1 mm long with coronoid process 50.7 mm high; no teeth preserved
Horizon
Khok Kruat Formation, Aptian, Early Cretaceous , 121.4–113.2 million years ago
Locality
Khok Kruat Subdistrict, Nakhon Ratchasima, Thailand

References

  1. Shibata, M.; Jintasakul, P.; Azuma, Y. (2011). A New Iguanodontian Dinosaur from the Lower Cretaceous Khok Kruat Formation, Nakhon Ratchasima in Northeastern Thailand. Acta Geologica Sinica (English Edition) 85(5): 969-976. Wiley. doi:10.1111/j.1755-6724.2011.00530.x shibata2011a
  2. Madzia, D.; Arbour, V. M.; Boyd, C. A.; Farke, A. A.; Cruzado-Caballero, P.; Evans, D. C. (2021). The phylogenetic nomenclature of ornithischian dinosaurs. PeerJ 9: e12362. doi:10.7717/peerj.12362

    Lists Ratchasimasaurus in Hadrosauroidea under the reference phylogeny of Madzia and colleagues (2019).

    madzia2021a
  3. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Treats it as a valid styracosternan.

    jones2026a
  4. Madzia, D.; Jagt, J. W. M.; Mulder, E. W. A. (2019). Osteology, phylogenetic affinities and taxonomic status of the enigmatic late Maastrichtian ornithopod taxon Orthomerus dolloi (Dinosauria, Ornithischia). Cretaceous Research 108: 104334. Elsevier BV. doi:10.1016/j.cretres.2019.104334

    Recovered Ratchasimasaurus within Hadrosauroidea, paired with Proa.

    madzia2019a